ReadKit initially answered the requests for a proper Instapaper and Readability desktop app, including Pocket and later adding support for popular bookmarking sites like Delicious and Pinboard. Bringing together the multiple places where people are likely to save stuff on the web, ReadKit 2.0 adds offline support for RSS to the mix, and also includes support for Fever and NewsBlur. But by far, my favorite feature is smart folders.
I have a big backlog of articles I have to read through in Pocket, but I'm only interested in a few topics at the moment. Smart folders act as ReadKit's playlists, bringing forward articles based a set of rules. For example, I can make sure I've caught up on all the games I like by looking for keywords in the title.
ReadKit 2.0 also adds a few new options for readers in the preferences, such the option to save and restore reading positions and to cache images locally. Under the hood you'll find improve sync performance and various other bug fixes.